The invention relates to sprockets for use with roller chains. Furthermore, the invention relates to a sprocket for use with roller chains to reduce noise related to chain and sprocket impacts as well as chordal motion. Moreover, the invention relates to a unique tooth profile of a sprocket which has a greater noise reduction than conventional sprockets.
Sprockets and roller chains are generally used in automotive transmissions, transfer cases and engine timing systems and the like. The sprockets currently used have various types of tooth profiles. For example, one widely used standardized type of sprocket has teeth with a pointed shape. The roots of this conventional sprocket have a profile shaped like an arc of a circle with a radius substantially corresponding to the radius of a roller of the chain and with a center of the roller radius located on the pitch circle of the sprocket.
In order to accomplish transmission of power, the teeth of the sprocket engage the rollers of the roller chain. Impact noise is generated as the rollers of the roller chain collide with and engage with the sprocket teeth of the sprocket. Additionally, noise is also generated by the vertical chordal motion of the chain as it engages the sprocket. This is due to the wrapping of the chain in a polygonal manner as it engages the sprocket. This wrapping causes the chordal action or vertical motion of the chain as it enters and exits the driving and the driven sprockets. The chordal action causes variations in the tension and the circumferential speed of the chain to occur as the chain is moving. As a result, fluctuation of the driving force on the driven shaft, angular velocity fluctuation of the driven shaft and increased noise are induced.
Previously there have been many attempts to reduce the noise in the operation of chains and sprockets. These various attempts in noise reduction included various designs to reduce the engagement or impact noise when the chain meets the sprocket as well as the noise generated by the chordal motion of the chain.
For example, silent chains have been utilized to reduce the noise generated by the chain and sprocket. Generally, these silent chains comprise of multiple link plates, each of which has a pair of inverted teeth and apertures. The links are interleaved or connected by connecting pins inserted in the apertures or pin holes. Each tooth of the link plate is composed of an inside flank and an outside flank. At least one flank of each tooth will engage with the sprocket teeth for the transmission of power to occur. The result is the transmission of power from the driving sprocket to the driven sprocket. Examples of silent chains can be found in U.S. Pat. No. 5,345,753, owned by the assignee of the instant invention.
Various modifications have been made to the silent chains themselves to further reduce the noise in the operation of the chain. For example, one type of silent chain utilizes links in a random arrangement of different configurations of the inside and outside flanks of the link plates. The shape or amount of protrusion of the inside flanks of the link plate teeth is made irregular in the lengthwise direction of the chain. In the alternative, the link for inner flank engagement and the link for the outer flank engagement are arranged randomly to achieve noise reduction. Another attempt to reduce the noise of the silent chain involved the modification of the engagement of the link plate and sprocket teeth. The number of link plate teeth that simultaneously engage the sprocket teeth is increased by either making the shape or amount of protrusion of the inside flanks of the link plate larger than that of the outside flank for all link rows.
In addition to changes to the chain and its structure to helps reduce the noise, modifications have also been made to the sprockets themselves in an effort to reduce the noise generated by the engagement of the chain and sprocket. For example in U.S. Pat. No. 4,758,209, the sprocket is formed of an even number of teeth with substantially equal radii and alternating tooth profiles. One tooth profile comprises outwardly converging flanks terminating in slightly rounded ends. The other tooth profile comprises involute curved flanks terminating in slightly rounded edges. This sprocket is used with block laced timing chains so that the outwardly converging flanks engage the inside flanks of the leading chain link teeth and the involute curved flanks engage the outside flanks of the trailing link teeth.
Another approach to reduction of noise in a chain drive mechanism can be found in U.S. Pat. No. 5,360,378. In this chain drive mechanism, rubber rings are provided on each of the side faces of a sprocket wheel. The rubber rings are coaxial with each other and the sprocket. The rubber rings do not come into contact with the chain as it rotates since there is a clearance between the peripheries of the rubber bodies and the inner edges of the pin link plates and the inner edges of the roller link plates.
U.S. Pat. No. 5,397,278, to Suzuki et al., describes the use of a sprocket for chains, such as conventional roller chains. The sprocket decreases the impact between the rollers of the roller chain and the sprocket during operation. The Suzuki et al., sprocket has a plurality of teeth with a bottom surface located between two adjacent teeth. Each tooth has a leading flank and a trailing flank. On the leading flank of one tooth and the trailing flank of the preceding tooth are two "meshing points" on which the roller of the chain seats without seating at the bottom of the root between the teeth. The distal surface of the leading face of a tooth, according to Suzuki et al., is defined by the envelope of circles of the same diameter as that of the rollers, which move according to a circumference that has a radius equal to the pitch between chain rollers and a center positioned in the center of a roller located in the adjacent space between teeth. Suzuki et al., do not address the noise due to the chain's chordal motion as the chain enters the sprocket.
This invention addresses the noise resulting from the operation of the chain and sprocket assembly by the design of the sprocket which addresses both impact noise and the noise generated by the chordal action of chain upon engagement with the sprocket. More particularly, the invention comprises a design for a sprocket tooth profile.